Stack switch



V. H. HARDY vSTACK SWITCH Nov. 17, 1942.

Filed Nov. 1. 1940 (Ittornegs Patented Nov. 17, 1942 UNITED STATiiS iftli'lhllli'l OFFICE STACK SWITCH corporation of Delaware Application November 1, 19410, Serial No. 363,868

6 Claims.

This invention relates generally to thermally actuated electric switches and more particularly to improvements in that type of switch which is known as a stack switch for use in a control system for fluid fuel burners.

Although the present embodiment is shown and described as a stack switch it will be apparent that the switch mechanism, as a whole or in part, may be used in other applications wherein it is desired to control an electric circuit or operate an electric switch by temperature changes.

One object of the invention is to provide a switch mechanism of simple construction which is positive and reliable in operation and in which the switch contacts will open or close with a snap action immediately upon initial expansion or contraction of the thermal element.

A further object is to provide a switch mechanism of this type in which an actuating member for the movable switch' contact is limited in movement and continued expansion or contrae tion of the thermal element will not affect the position thereof after such actuating member has been moved to open or close the switch contacts upon initial expansion or contraction of away, taken substantially on line 2-2 of Figure 1;

Figure 3 is an enlarged, fragmentary. sectional View taken substantially on line 3 -3 of Figure 2.

For a more complete understanding of one application of the present invention there has been shown in Figure l an oil burner control unit embodying my stack switch. Such oil burner control unit may be generally of conventional construction and include such elements as the relay 2, safety reset switch 4, and starting switch 6 which constitute no part of the present invention. Such control elements, together with my improved stack switch, may be conveniently mounted on the base 8 and enclosed by the removable cover Il).

A bracket l2 secured to the rear side of the base connected to a sleeve i4 which may be secured in any desired manner to a combustion chamber ""lu. 'tion block 34 of substantially U form is adaptedL w. by an end wall 24.

(Cl. 20D- 137) wall or flue i6 to support thev control unit with the thermal element or elements of the stack switch extending through the sleeve l into the combustion chamber or ue so as to be subject to .:ponent parts thereof are secured to or :'nounted on a bracket, indicated generally at i8, which is .formed as a channel with areal' wall 2li adapted to be secured to the base plate Band with parallel side walls 22 with one end of the channel closed open end secured to the rear wall 2Q of the bracket I8 and extends rearwardly therefrom. The rear or outer end of the tubular member 26 is closed by a cap 28 to which is secured one end of the rod 30 which extends through the tubular member and projects through the open end thereof with the relatively free inner end of the rod 30 supported for substantially axial movement by a ilexible strap 32 connected to this end of the rod and to the end wall 24 of bracket i8.

As will be obvious to those skilled m the art, the tubular member 26 and rod 3Q are constituted of materials having decidedly different heat expansion characteristics so that the differential expansion thereof on changes of temperature will cause a substantially axial movement of the inner end of the rod 3B which is utilized to operate the l switch per se in a manner to be hereinafter described. In the present instance applicant has employed in actual practice an alloy with high heat expansion and good heat and corrosion resistance such as an iron alloy containing about 18% chromium and 8% nickel for the tubular member 26, and an alloy of low heat expansion such as the iron alloy known as invar containing about 36% nickel for the rod 30.

The outer ends of the thermal elements.com-` prised of the tubular member 25 and rod 30 arev adapted to be extended in the particular application disclosed herein into the combustion space or flue so that the same will be subjected to the heat of the combustion or flue gases and with the alloys mentioned above, or generally similar alloys, lt will be apparent that when heated, the

' tubular member 25 will expand lengthwise to a greater extent than the rod 36 and thereby cause an inward movement of the relatively free inner end of the rod 30.

A switch operating member consisting of a frio- A tubular member 2li has its to be frictionally engaged with the rod 30 adjacent the inner end thereof and within the bracket I8. As shown in Figures 1 and 2 this block 34 engages one side of the rod 3U and the spaced arms of the block extend on the opposite side of the rod and receive the ends of a triangular pin 36 which provides a knife edge extending at right angles to the axis of the rod and spaced therefrom.

The side walls 22 of bracket i8 are provided with aligned openings 38 which are each formed with a V-shaped notch to function as a bearing or fulcrum 4e for a knife edge on one of the spaced arms 42 of a contact lever 44. An insulating plate 46 is secured to the contact lever 44 and carries a contact spring 43 having a Contact il!) secured thereto adjacent its free end. The spring 48 is tensioned to force said contact 5f; away from the plate 45 but the extent of relative movement is limited by the hook portion 52 on the end of spring 48 which extends around the adjacent end of the plate.

The relatively movable contact 50 is adapted to cooperate with relatively stationary contact 54 mounted on an angle member 56 secured to one of the side walls Z2 of the bracket i8 `and insulated therefrom as indicated at 58. The contact engagement limits movement of the contact lever 44 in one direction and the movement thereof in the opposite direction may be limited by means suoli as a screw E adjustably secured to the wall 2! of bracket I8 and adapted to engage the insulating plate 46.

The contact lever 44 is formed with an opening 62 providing a knife edge E4. A U-shaped spring 66 is formed at one end with an inwardly facing groove adapted to be engaged with the knife edge 64 on contact lever 44, and is similarly formed at the other end with an inwardly facing groove adapted to be engaged with the knife edge of the triangular pin 36.

As will be apparent from the showing in Figure 1, the several parts of the contact mechanism are assembled so that the arms 42 of the contact lever engage the aligned fulcrums 43, and the spring 86 which is so constituted that the ends thereof tend to approach one another, functions to tension the friction block 34 against the rod 3l! and hold the arms 4?. of the contact lever 44 against the fulcrums 4Q. This spring 6E also functions to move the contact lever 44 in both directions around the fulcrums 40 with practically snap action when the switch is operated in the manner now to be described.

It will rst be noted that the knife edge of pin fulerums 40, and knife edge B4 are substantially in alignment, or in other words, located in the same planel which plane extends at right angles to the rod 33, and that the fulcrums 4D are relatively fixed whereas the knife edge of pin 3S and the knife edge S4 are movable relative thereto. If these points of engagement are exactly in line, the force exerted by spring 6B would not tend to throw the Contact lever 44 to either side of such line. but if the pin 35 should be moved outl of linethe spring 66 would cause the Contact lever to move about fulcrums 40 to one or the other side and contacts 50 and 52 would be opened or closed with a snap action.

In Figure 1 the contacts 50 and 54 have been .shown as closed which is the normal position vhen the fiuid fuel burner is not in operation. In this position it '-.vill be seen that the knife edge cn pin 3S is slightly to one side, or below as viewed in Figure 1, an imaginary line passing through fulcrum 4U and knife edge 54 and spring 65 is exerting tension on contact lever 44 in a direction to hold contact 50 in engagement with Contact Assuming now that the burner is started, the heat of combustion or flue gases will cause a substantially axial movement of the in ner end of rod 3S in the manner heretofore described and the frictional engagement of rod 3D with block 34 will cause the latter to also move with the rod and thereby move the pin 36 upwardly as viewed Figure l. Then as soon as the knife edge of pin 33 moves beyond or above the imaginary line passing `through the fulcrum 40 and knife edge f5.4, the spring 66 will exert a tension on contact arm i4 to move the same about fulcrum 4S with a snap action to break contacts 5C and 54.

As been heretofore mentioned, it is desired that the swi h conto cts be opened or closed subs'eitially immediately upon any initial rise or l. in temperature such as causes expansion or contraction of the thermal elements, regardless of the extent of actua? temperature changes. To obtain this result the friction block 34 is limited in its extent of movement axially of the rod 30 by forming the block 34 with a slot E8 extending transverse to the axis of rod 3D and parallel to the axis of pin 3G and providing a limit pin 'l0 which is received within the slot |58. The slot 58 is slightly wider than the diameter of the pin T0 which is relatively fixed so that the friction block 34 can move only to an extent determined by the clearance between the sides of the slot and the pin.

The limit pin i0 is preferably eccentrically iocated on the hexagonal end of a screw 12 extending through end wail 24 of bracket I8, and an adiusting lever I4 extending through a slot 16 in one of the side walls 22 of bracket I8 may be provided to rotate the screw 12. The primary purpose of this arrangement is to provide for relatively minor adjustments of the initial position of the friction block 34 on rod 30 such as may be necessary to properly line up the pin 35 with reference to fulcruins 4@ and knife edge 64. This adjustment. may be found necessary due to misalignment which may develop during extended use but is particularly useful during asn sembly since the relative movement of the friction block to operate the switch in opposite drections is so slight that extreme accuracy would otherwise be required in the manufacture and assembly of the several parte of the switch anis-m for each unit.

After adjusting the position of the block 34 by rotation of the screw 'l2 and its eccentrically lecated limit pin l0, the latter may be held in the desired position to thereafter merely limit the extent of movement of the friction blc l by tightening both the nut T8 on screw 'l2 nd a guide screw 8f3 on lever .14 which extends thro rh an arcuate slot 82 in the end wall 24 of bracket I8. It should be noted that Figure 3 docs not show the same relative location of limit pin '.'0 as is shown in Figure 1. but illustrates merely one position of the adjusting lever i4 in lull l? and a further position thereof in dot and d. tu lines.

From the foregoing it will be understood that after such movement of the friction block 31?- by the rod 30 in one direction within the limits dcned by the slot 68 and limit pin 7n as is necessary to operate the switch Contact 50 to either open or closed position in the manner hereticfore described, the inner end of rod 3B may con 1 SLECH- tinue its substantially axial movement in that direction on continued expansion or contraction, whichever the case may be, and slide within the friction block 3d, but just as soon as the temperature first starts to rise or fall, the initial movement of the inner end of rod 39 in an opposite direction will cause an immediate movement of the lfriction block to cause the spring 66 to actuate the switch contact with a snap action to an opposite position.

Having described one embodiment of my invention, it is desired to mention various changes which will be apparent to those skilled in the art without departing from the spirit and scope of the invention. It will, of course, be understood that other alloys than those mentioned herein which have a diiierence in their heat expansion characteristics may be employed for the thermal elements consisting of the tubular member 26 and rod 3i) depending upon the time of response and extent of movement desired for the inner end of rod 3i) in any particular use. It will further be understood that the rod 30 could be moved axially by the provision of some separate element such as a bimetallic loop or such other thermal elements as are known in the art.

It will also be apparent that a further set of contacts could be substituted for the limit screw 60 or the relative positions of contacts 50-54 and limit screw 50 interchanged so that the circuit to be controlled thereby would be closed on rise in temperature instead of opened as described herein. Whereas the present invention has been disclosed as a stack switch, the several features thereof are not limited to this particular use but may be employed in many known types of temperature controls,

Many other changes and modifications in the specific construction disclosed herein will be apparent to those skilled in the art and are contemplated as within the scope of my invention as set forth in the claims.

I claim:

1. In a thermally oper-ated switch, a rod having a portion thereof movable axially in response to temperature changes, cooperating contacts, and means whereby one of said contacts may be moved into and out of engagement with the other contact upon axial movement of said rod including a friction block adapted to engage said rod, and means to limit the extent of movement of said block axially of said rod comprising a slot in said block and a relatively xed limit pin adapted to engage loosely within said slot and limit the movement of said block by contact with the sides of said slot.

2. The combination set forth in claim l wherein said limit pin is mounted for adjustment along the axis of said rod.

3. The combination set forth in claim l wherein said limit pin is carried by a rotatably adjustable member and eccentric to the axis of said member whereby rotation ci said member will adjust said pin along the axis of said rod.

Li. In a thermally operated switch, a thermal element, a rod movable axially by said thermal element, a friction block adapted to engage one side of said rod, a knife edge on said block on the opposite side of said rod, a contact lever having a contact adjacent one end thereof adapted to cooperate with a relatively fixed contact, a fixed fulcrum adapted to be engaged by the other end of said contact leverx a ki .ie edge on said lever intermediate the ende thereof, and a substantially U-shaped spring having its ends engaging said knife edges and adapted to hold said block in frictional engagement with said rod and hold said lever in engagement with said fulcrum and operate said lever carried contact into and out oi engagement with said relatively iixed contact with snap action on movement of said block in opposite directions by said rod.

5. rihe combination set forth in claim 4 wherein an adjustable stop member is provided to limit movement of said Contact lever away from said relatively fixed contact, and means is also provided to limit the movement of said friction block to a relatively narrow range while permitting continued movement of said rod in either direction.

6. In a thermally operated switch, a rod having a portion thereof movable axially in response to temperature changes, cooperatingr contacts, means whereby one of said contacts may be moved into and out of engagement with the other contact upon axial movement of said rod portion including a friction block adapted to engage said rod and means connecting said block to said movable contact to operate the same upon the initial movement of said block in either direction, and adjustable means cooperating with said block to limit the extent of movement of said block axially of said rod and provide for initial axial adjustment of the position of said block on said rod.

VAUGHN H, HARDY, 

